Dynamics of electric field screening in a bulk GaAs modulator

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Abstract
The transient development of electric-field distributions in a biased GaAs film after low-density optical excitation is determined by measurements of Franz-Keldysh modulations with a time resolution of 100 fs. The experimental results are compared with theoretical calculations. The transient field is calculated with a drift-diffusion model. Our calculation of the dielectric function of GaAs includes the Coulomb coupling and the electric field. The resulting optical transmission changes are calculated with a transfer-matrix method. The theory predicts a modification of the Franz-Keldysh modulation due to the nonuniform field, in quantitative agreement with the experimental observations.